It is now the usual case that the small transducers on disk memory units employing rigid disks are carried by an arm which is rotatably mounted to the deck which holds the disk spindle itself. The arm is positioned by a powerful permanent magnet motor which rotates the arm to position the transducer on the disk at the desired radius. The motors are typically designed with extremely high torque so that actuation, i.e. movement from one radius to another, of the arm occurs as quickly as possible.
High torque requires high strength magnets. The magnets are usually made from a boron rare earth metal (such as samarium or neodymium) alloy and have extremely high flux generating capability. When fully magnetized, they are so powerful that a normal person cannot manually restrain the magnets from slamming onto the pole piece which mechanically supports them, or into each other, with such force that the magnet itself is shattered by the impact, causing pieces to fly dangerously around the area and damage the magnet beyond use. And if a person is unlucky enough to get a finger between such a magnet and any ferrous object, serious injury is possible.
In one particular actuator motor design, a pair of such magnets are coated with a thermosetting glue and then mounted in required, spaced-apart positions, on a common surface of a pole piece. The magnetic attraction between the magnets and the pole piece allows the magnet-pole piece assembly to be transported without shifting of the magnets on the pole piece to an oven for baking to mechanically bond the magnets to the pole piece.
Two magnet pairs are used to define between them a flux carrying gap in which the coil of the actuator motor moves in response to current passed through it. The coil is attached to the transducer arm, and in this way the arm is rotated to place the transducers at the desired radius.
A serious problem, alluded to above, is how one attaches and properly positions the magnets on the pole pieces without risking one's limbs or damaging the magnets. Once they have attached themselves to the pole piece, if they are not positioned properly, it is remarkably difficult to reposition them before baking. While repositioning can be done manually, or even with a tool, when thousands of these assemblies are needed for a production run, it is simplest to assure that the magnets are attached accurately at the very beginning.
There appears to be very little in the literature which addresses these problems. There are a number of patents which deal with various aspects of assembling conventional rotary electric motors. Among these, roughly in the order of their relevance, are U.S. Pat. Nos. 4,586,244; 4,608,752; 4,644,640; 4,126,933; and 4,443,934.